Retinal pigment epithelium (RPE) cells and photoreceptor cells are functionally and developmentally closely integrated. Derangements of the RPE are involved in certain retinal diseases. However, the RPE is poorly understood at the molecular level. We have cloned and characterized RPE65, a novel developmentally-regulated conserved 65 kDa RPE-specific microsomal membrane-associated protein. The cDNA sequence is being used to overexpress RPE65 protein for functional studies. The potential role of th protein in inducing uveitis will also be studied using recombinant protein. The RPE65 protein is not expressed in cultured RPE even though its mRNA is abundant. In characterizing this example of posttranscriptional regulation, we have identified distinct sequences in the 3~ untranslated region of the RPE65 mRNA that control the stability and the efficiency of translation of the RPE65 message. We have cloned and are sequencing a full-length human genomic clone for RPE65. It is at least 40 kilobases in length. Sequence analysis shows that the RPE65 protein is highly conserved between human and cow. We have also cloned the mouse gene. The human gene for RPE65 is localized to chromosome 1p31, and the mouse homolog to distal chromosome 3. These do not correspond to any ocular disease gene localized so far. Nonetheless, RPE65 remains a candidate gene for RPE- involved disease.